The invention relates to a compound needle, in particular for loop-forming textile machines.
A compound needle is know from DE 25 37 502. It has an elongated based body, which makes a transition into a hook at one end. Two slit walls, which are arranged spaced apart and parallel, start at a location opposite the open side of the hook and extend along the shank. A slider slit is formed between the slit walls. A slider, which can be longitudinally displaced and consists of two slider springs resting flat against each other, is arranged in the slider slit. The springs are approximately rectangular in cross section. The slider can touch the hook, or at least a hook tip, with its upper corner section when the slider is displaced in the direction toward the hook. For this purpose, the two slider springs are slightly bent away from each other on their corresponding upper corner sections in order to form in this way a funnel for receiving the hook tip. This funnel opens in a direction obliquely in respect to the movement direction of the slider.
In order to let both outward bent corners of the slider enter into the slider slit, the latter is widened in an upper narrow strip-shaped section. But the section of the slit close to the bottom is narrower. The bottom of the slider slit is substantially level, the slider performs a purely axial movement, in the course of which the slider is provided with guidance in every position by the inner faces of the slit wall, whose distance is uniform.
A compound needle is furthermore known from DE 199 13 822 C2, whose characteristic feature resides in the design of the slider. The latter is constituted by two slider springs which are convexly bent away from each other. They are again bent away from each other at their two free ends facing the hook in order to form a receiving funnel for the hook tip. Good centering of the slider springs in the slider slit is achieved by the lateral bulge of the slider springs.
Because of their tendency to spring away from each other, the slider springs rest resiliently against the slit walls.
Guidance of the slider has been proven to be especially good if the slider slit is narrow, so that the slider springs are well centered. Because of this the slider is also relatively insensitive against a lateral pull emanating, for example, from obliquely extending loops.
For its movement the slider requires a force which overcomes the slider friction in the slider slit. The slider friction is a function of the funnel size, for example. If the slider springs are spread far apart at their free ends, so that a large funnel is formed, which also assuredly meets the hook even at lateral yarn tension, an increased slider friction results.
A further problem lies in that the slider friction is considerably increased when dirt, fiber remnants and the like enter into the slider slit. This can lead as far as to the compound needle becoming inoperative.
It is the object of the invention to create a compound needle which is only a little, or not at all sensitive to lateral yarn tension and has reduced slider friction.
This object is attained by means of a compound needle having the characteristics of claim 1.
The compound needle of the invention has a slider with at least two slider springs running in a slider slit. The slider can be made of one piece or of several individual elements (slider spring, slider body), which are releasably or permanently connected with each other. On its end facing the hook, the slider slit is narrower in a first guide section than in the remaining section. The width or (synonymously) breadth of the slider slit is greater in the second guide section than in the first guide section, each measured at the same height over the needle back. If both measuring locations M1, M2 are connected with each other via an imagined straight line G, this straight line G extends parallel with the needle back (FIG. 4). The first guide section is narrower over its entire height than the second guide section adjoining the first guide section in the longitudinal needle direction. In addition, each of the slider springs is convexly curved toward the outside. The width of the slider slit is embodied to be stepped in the longitudinal direction. At its inlet (a location at the front in the longitudinal direction) it is narrow and, remote from the inlet (a location at the back in the longitudinal direction), it is wide in its second guide section, i.e. it is narrower in the vicinity of its inlet located directly opposite the hook than in the remainder. Both guide sections can partially overlap. It is also conceivable for the slider slit, or at least the second guide section, to assume a stepped embodiment shape, or one deviating from a U-shape, partially or over its entire length.
The lateral bulge of the slider springs is preferably fixed in such a way that it is located in the narrowed slider section when the free ends of the slider springs, which form a funnel, are pushed over the hook tip. The length of the narrowed section and the position of the convex sections of the slider springs are fixed in such a way that, when the slider is pushed in the direction toward the hook, the convex sections of the slider springs enter the narrowed slit section before the funnel reaches the hook tip. By means of this the funnel is precisely centered shortly before arriving at the hook tip, so that it can be kept very narrow and meets the hook centered, despite lateral yarn tension. On the other hand the slider friction is generally low because, as soon as the slider is pulled back from the hook, the laterally convex slider spring sections come into the widened slit, in which they run on the slit walls at low spring tension or even with play.
Dirt and fiber remnants can also be deposited in the widened slit section (second guide section) without the ability of the compound needle being affected too much. Thus, the compound needle in accordance with the invention is less susceptible to soiling.
The fact that the free ends of the slider springs forming the funnel spread away from each other as soon as the convex section of the slider springs enters the narrowed slit section constitutes an additional effect which permits a particularly narrow outlay of the funnel. There, the convex section of the slider springs are moved toward each other (pressed together), because of which the free ends of the slider springs can be spread away from each other to a width which exceeds the slit width. By means of this it is possible to assure a particular dependable working of the compound needle.
The curvature of the slider springs is preferably of such a size that the outer funnel width is approximately as large as the slit width of the slider slit or slot when the convex sections of the slider springs are located in the widened section of the slider slit. This assures a low slider friction, because the slider springs can relax in the slider slit. Preferably the convex sections rest without bias in the widened slit.
The slider friction at the slit flanks is essentially limited to the narrow front slit section. A high moment of resistance against lateral loop tension, as well as low friction, i.e. a smooth moving slider, is achieved by means of this.
The compound needle has an arrangement which, when the slider is retracted, causes it to dip into the slider slit. As known per se (for example from WO 01/311010), the slider slit has a bottom guide surface for guiding the slider elements at its inlet for this purpose. This forms a movement base for the slider springs. A recessed bottom area is provided adjoining this movement base, which is at a lesser distance from the needle back than the bottom guide surface. With an identical height of the slit wall, this results in a depression in the slider slit. Viewed from the inlet of the slider slit, the bottom guide surface first extends straight at a slightly greater distance from the needle back, and then approaches to the needle back and extends parallel with the needle back at a lesser distance from the needle back. Because of this the slider spring can dip at the same time it is retracted, i.e. be pulled back into the deepened slider slit area below the upper slit wall edge. This has meaning in connection with particularly fine knit goods, wherein small loops are to be formed and a low shank height, as well as only a small increase in the shank height in the direction away from the hook, is desired. At the location where the bottom guide surface ends and the slit bottom extends downward toward the needle back, the slider preferably enters the slider slit with the tips of its slider springs. A total of three guide surfaces are formed at the slit inlet in this way. These are the two oppositely placed inner faces of the slit wall and the bottom guide surface between them. Together, these three surfaces form a guide means or a guide arrangement and, in respect to the funnel spreading, simultaneously an actuating means. The latter, because the inner faces of the slit wall compress the slider springs as soon as the convex sections of the latter enter between them. The remaining slit is used as a guide space into which the slider can be retracted and runs with litter friction or with play. Precise guidance of the slider is only provided when its slider springs forming the funnel exit the slider slit, i.e. when its convex sections which spring away from each other move to the inlet in the first guide section.
As known from WO 01/31101), a cam guide can be provided on the needle body for controlling the dipping of the slider into the slider slit, which is engaged by correspondingly curved sections of the slider springs when the slider is retracted. The roller neck guide is constituted, for example, by two guide surfaces provided on the needle body, which are arranged obliquely in respect to the needle body, and to which guide surfaces of the slider spring oriented at the same angle are assigned. In the course of retracting the slider, the guide surfaces come into contact with each other and cause a downward movement of the slider, so that it dips into the slider slit (and therefore nears the needle back).